Phase grating with three-dimensional configuration

ABSTRACT

A phase grating includes a substrate and a first dielectric layer. The first dielectric layer is disposed on the substrate and includes a column and a plurality of rings. The top sides of the column and the top sides of the rings align with one another to form a flat plane. The column and the rings are concentric.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims the benefitof U.S. patent application Ser. No. 13/310,808, filed Dec. 5, 2011 andentitled “PHASE GRATING WITH THREE-DIMENSIONAL CONFIGURATION”. patentapplication Ser. No. 13/310,808 is a continuation application of andclaims the benefit of U.S. patent application Ser. No. 12/255,642, filedOct. 21, 2008 and entitled “METHOD FOR FORMING PHASE GRATING”. Theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a phase grating. In particular, thepresent invention relates to the phase grating with rings which havedifferent heights.

2. Description of the Prior Art

Grating is an optical element made of periodical fine patterns. Thepatterns constituting the grating may be the change of transmittance,thickness or index of refraction. Among which, the grating made ofchange of thickness or index of refraction modulates the phase of thelight to have diffraction. It is therefore called “phase grating”.

The substrate for the grating is usually glass or plastics. Thetransmittance, thickness or index of refraction of the surface is thensomehow changed. For example, fine patterns are engraved on the glasssubstrate by mechanical methods to obtain a reflective grating. Besides,most of the gratings made of plastics are thickness modulation type.First, a mother mold made of metal material is produced then theproducts are replicated therefrom. The problems of this method are, forexample, difficult to control the cross section of the patterns and lowyield.

For instance, the conventional Fresnel Lens is known to have the abilityto focus without the disadvantages of traditional glass lens, such asheavy weight and bulky size. The Fresnel Lens per se may be composed ofsheets made from polymeric materials with its surface engraved withmultiple concentric circles. The angles and thickness of each circle isdifferent so the Fresnel Lens is able to focus light.

First, U.S. Pat. No. 5,132,843 discloses a grating lens. Such gratinglens is composed of a plurality of concentric circles formed on thesurface. However, U.S. Pat. No. 5,132,843 does not disclose thesubstrate is made of what material or a plurality of concentric circlesis formed by which methods on the substrate. Besides, U.S. Pat. No.6,570,145 discloses another phase grating imaging sensor and the methodfor making the same. U.S. Pat. No. 6,570,145 discloses that a pluralityof concentric circles is formed on a metal material, such as Cr, toobtain the phase grating imaging sensor. The aforesaid phase gratingsare Fresnel Lens. The lens of such Fresnel Lens type phase gratings areof the same depth and disposed on the same surface. The focus capabilityof such planar gratings is not optimal. Accordingly, a phase grating ofbetter focus capability is needed to overcome the problems which theFresnel-Lens type phase grating encounters in the semiconductor field.

SUMMARY OF THE INVENTION

The present invention therefore proposes a Fresnel-Lens type phasegrating of better focus capability. Such Fresnel-Lens type phase gratingof the present invention which is disposed above an image sensorpossesses excellent focus capability due to different depths of its lensand to the three-dimensional configuration. The phase grating of thepresent invention not only exhibits the advantage of the Fresnel-Lensbut also avoids the disadvantages of the traditional complicatedprocesses to form semiconductor optical elements, such as micro lens orcolor filters. In such way, the problems which the Fresnel-Lens typephase grating encounters in the semiconductor field are overcome. Still,the micro optical elements, such as the CMOS image sensor (CIS) in thesemiconductor field may also utilize the vantage point of theFresnel-Lens type phase grating well.

The first aspect of the present invention proposes a phase grating. Thephase grating includes a substrate, a first dielectric layer and asecond dielectric layer. The first dielectric layer has a recess with atapered side on the substrate. The second dielectric layer is disposedon the recess with the tapered side and on the first dielectric layerand includes a column and a plurality of rings. The top sides of thecolumn and the top sides of the rings align with one another to form aflat plane. The column and the rings are concentric and the rings aredisposed on the tapered side of the recess so that the height of eachring is different.

In one embodiment of the present invention, the substrate includes animage sensor to correspond to the phase grating.

In another embodiment of the present invention, the first dielectriclayer and the second dielectric layer have different etchingselectivity.

In another embodiment of the present invention, the phase gratingfurther includes an etching-stop layer disposed on the first dielectriclayer.

In another embodiment of the present invention, the etching-stop layermay be nitride, oxide or oxynitride.

The second aspect of the present invention proposes another phasegrating. The phase grating also includes a substrate, a first dielectriclayer and a second dielectric layer. The first dielectric layer has abulge with a tapered side on the substrate. The second dielectric layerdisposed on the first dielectric layer and comprises a column and aplurality of rings. The top sides of the column and the top sides of therings align with one another to form a flat plane. The column and therings are concentric and the rings are disposed on the tapered side ofthe bulge so that the height of each ring is different.

In one embodiment of the present invention, the substrate includes animage sensor to correspond to the phase grating.

In another embodiment of the present invention, the first dielectriclayer and the second dielectric layer have different etchingselectivity.

In another embodiment of the present invention, the phase gratingfurther includes an etching-stop layer disposed on said first dielectriclayer.

In another embodiment of the present invention, the etching-stop layermay be nitride, oxide or oxynitride.

The third aspect of the present invention proposes another phasegrating. The phase grating includes a substrate, a first dielectriclayer and a plurality of annular trenches. The first dielectric layer isdisposed on the substrate and includes a column and a plurality ofrings. The top sides of the column and the top sides of the rings alignwith one another to form a flat plane. The column and the rings areconcentric. A plurality of annular trenches are respectively sandwichedbetween the column and the rings so that the depths of any two annulartrenches which are adjacent are different.

In one embodiment of the present invention, the substrate includes animage sensor to correspond to the phase grating.

In another embodiment of the present invention, the annular trenchesrespectively have different width.

In another embodiment of the present invention, the closer to theconcentric center the smaller the width is.

In another embodiment of the present invention, the closer to theconcentric center the greater the depth is.

The phase grating of the present invention possesses excellent opticalproperties and focus capability due to different depths of its lens andto the three-dimensional configuration. The phase grating of the presentinvention not only exhibits the advantage of the Fresnel -Lens but alsoavoids the disadvantages of the traditional complicated processes toform semiconductor optical elements, such as micro lens or colorfilters. In such way, the problems which the Fresnel-Lens type phasegrating encounters in the semiconductor field are overcome.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 illustrate a preferred embodiment of the method for forming aphase grating of the present invention.

FIGS. 8-10 illustrate another preferred embodiment of the method forforming a phase grating of the present invention.

FIGS. 11-14 illustrate still another preferred embodiment of the methodfor forming a phase grating of the present invention.

FIG. 15 illustrates a cross sectional view of the phase grating of thepresent invention.

DETAILED DESCRIPTION

The gist of the present invention provides a method to practice variousphase gratings to obtain a Fresnel-Lens type phase grating of betterfocus capability. Such Fresnel-Lens type phase grating of the presentinvention not only possesses excellent focus capability but also avoidsthe disadvantages of the traditional complicated processes to formsemiconductor optical elements, such as micro lens or color filters,which is particularly suitable for the micro optical elements, such asthe CMOS image sensor (CIS) in the semiconductor field.

The present invention first provides a method for forming a phasegrating. FIGS. 1-7 illustrate a preferred embodiment of the method forforming a phase grating of the present invention. As shown in FIG. 1,first a substrate 101 is provided. The substrate 101 may include Si. Inaddition, the substrate 101 further includes a micro optical element,such as an image sensor element 102. A first dielectric layer 110 isformed on the substrate 101, so that the first dielectric layer 110 hasa recess 111 with a tapered side 112. For example, a first procedure toform the first dielectric layer 110 having a recess 111 with a taperedside 112 may be, as shown in FIG. 2, a patterned layer 103 is firstformed on the substrate 101. Then, as shown in FIG. 1, a chemical vapordeposition, such as a high density plasma (HDP) is carried out so thatthe first dielectric layer 110 is formed. The resultant first dielectriclayer 110 not only covers the patterned layer 103, but also forms arecess 111 with a tapered side 112. The structure of the recess 111 withthe tapered side 112 of the first dielectric layer 110 is obtained withthe help of the contour of the patterned layer 103 by adjusting thedeposition/sputter ratio of the HDP chemical vapor deposition. Oralternatively, a second procedure to form the first dielectric layer 110having a recess 111 with a tapered side 112 may be first forming thefirst dielectric layer 110 then carrying out a selective etching toobtain the first dielectric layer 110 having a recess 111 with a taperedside 112. The patterned layer 103 may include a metal or a nitride, suchas silicon nitride. If the patterned layer 103 is composed of an opaquematerial, it may serve as the black matrix (BM) surrounding the imagesensor element 102. The method to form the patterned layer 103 may befirst blanket depositing a material layer on the substrate 101 then theneeded patterned layer 103 is formed by lithography and etching.

Second, as shown in FIG. 3, a second dielectric layer 120 is formed onthe first dielectric layer 110. The second dielectric layer 120 fillsthe recess 111 with the tapered side 112 and covers the first dielectriclayer 110. The tapered side 112 may have different slopes to deal withdifferent optical applications, for example different colors such as red(R) , green (G) or blue (B) . The materials for the second dielectriclayer 120 or for the first dielectric layer 110 may be the same ordifferent. For example, materials of different etching selectivity, forexample an oxide with a nitride, may be paired. The following is anexample of materials of different etching selectivity.

The second dielectric layer 120 is selectively etched to form the phasegrating of Fresnel-Lens structure which is disposed above the imagesensor element 102. The procedure to carry out the selective etching maybe that, as shown in FIG. 4, first an auxiliary selective etching mask140 is formed on the second dielectric layer 120 to facilitate theselective etching. FIG. 5 illustrates a top view of the selectiveetching mask 140 placed on the second dielectric layer 120 . Theselective etching mask 140 is placed on the second dielectric layer 120and includes a center circle 141, and a plurality of concentric rings142 alternating with the grating zones 143 which are not covered by theselective etching mask 140. Later, the second dielectric layer 120 isetched, as shown in FIG. 6. Because the materials for the seconddielectric layer 120 and for the first dielectric layer 110 havedifferent etching selectivity, the second dielectric layer 120 is etchedall the way to expose the recess 111 with the tapered side 112 of thefirst dielectric layer 110. Next, the selective etching mask 140 isremoved and the phase grating 130 is obtained.

If the materials for the second dielectric layer 120 and for the firstdielectric layer 110 have no etching selectivity, an etching-stop layer104 is formed on the first dielectric layer 110 before the seconddielectric layer 120 is formed, as shown in FIG. 7. The etching-stoplayer 104 may be made of materials such as nitride, oxide or oxynitrideas long as the etching-stop layer 104 and the second dielectric layer120 have distinctive etching selectivity. If it is the case, the seconddielectric layer 120 is etched all the way to expose the etching-stoplayer 104 and to obtain the phase grating 130.

Please refer to FIG. 6. The phase grating 130 includes a column 131 anda plurality of rings 132 . The plurality of rings 132 alternate with theFresnel grating zones 133. The width of the rings 132 or the width ofthe Fresnel grating zones 133 may be the same or different . The column131 and the rings 132 are concentric. In addition, the rings 132 aredisposed on the tapered side 112 of the recess 111 so that the height ofeach one of the rings 132 is different. This three-dimensionalconfiguration results in the depths of each Fresnel grating zones 133 tobe substantially different so the Fresnel-Lens type phase grating 130 ofthe present invention possesses excellent optical properties and focuscapability. In such way, the phase grating 130 of the present inventionnot only exhibits the advantage of the Fresnel-Lens but also avoids thedisadvantages, such as heavy weight and bulky size of the traditionalcomplicated processes to form semiconductor optical elements, such asmicro lens or color filters.

The present invention again provides another method for forming a phasegrating. FIGS. 8-10 illustrate another preferred embodiment of themethod for forming a phase grating of the present invention. As shown inFIG. 8, first a substrate 201 is provided. The substrate 201 may includeSi. In addition, the substrate 201 further includes an image sensorelement 202. A first dielectric layer 210 is formed on the substrate201, so that the first dielectric layer 210 has a bulge 211 with atapered side 212. For example, a first procedure of the presentinvention to form the first dielectric layer 210 may be that a patternedlayer 203 is first formed on the substrate 201. Then, a chemical vapordeposition, such as a high density plasma is carried out andsimultaneously adjusting the deposition/sputter ratio of the HDPchemical vapor deposition so the resultant first dielectric layer 210not only covers the patterned layer 203, but also forms a structure of abulge 211 with a tapered side 212 with the help of the contour of thepatterned layer 203. Or alternatively, a second procedure to form thefirst dielectric layer 210 may be first forming the first dielectriclayer 210 then carrying out a selective etching to obtain the firstdielectric layer 210 having the bulge 211 with the tapered side 212.

Second, as shown in FIG. 9, a second dielectric layer 220 is formed onthe first dielectric layer 210. The tapered side 212 may have differentslopes to deal with different optical applications, for exampledifferent colors such as red (R), green (G) or blue (B). The materialsfor the second dielectric layer 220 or for the first dielectric layer210 may be the same or different. For example, materials of differentetching selectivity, for example an oxide with a nitride, may be paired.The following is an example of materials of different etchingselectivity.

The second dielectric layer 220 is selectively etched until the firstdielectric layer 210 having the bulge 211 with the tapered side 212 isexposed to form the phase grating which is disposed above the imagesensor element 202. Please refer to the previous descriptions for theprocedure to carry out the selective etching and the details will not bediscussed here.

Please refer to FIG. 7. Similarly, if the materials for the seconddielectric layer and for the first dielectric layer have no etchingselectivity, an etching-stop layer is formed on the first dielectriclayer before the second dielectric layer is formed. The etching-stoplayer may be composed of materials such as nitride, oxide or oxynitrideas long as the etching-stop layer and the second dielectric layer haveetching selectivity. If it is the case, the second dielectric layer isetched all the way to expose the etching-stop layer and accordingly toobtain the phase grating.

Please refer to FIG. 10. The phase grating 230 includes a column 231 anda plurality of rings 232. The phase grating 230 is disposed above thecorresponding image sensor element 202. The plurality of rings 232alternate with the Fresnel grating zones 233. The width of the rings 232or the width of the Fresnel grating zones 233 may be the same ordifferent. The column 231 and the rings 232 are concentric . Inaddition, the rings 232 are disposed on the tapered side 212 of thebulge 211 so that the height of each one of the rings 232 is different.This three-dimensional configuration results in the depth of eachFresnel grating zones 233 to be substantially different so theFresnel-Lens type phase grating 230 of the present invention possessesexcellent optical properties and focus capability. In such way, thephase grating 230 of the present invention not only exhibits theadvantage of the Fresnel-Lens but also avoids the disadvantages of thecomplicated processes to form semiconductor optical elements, such asmicro lens or color filters.

The present invention still provides another method for forming a phasegrating. FIGS. 11-14 illustrate still another preferred embodiment ofthe method for forming a phase grating of the present invention. Asshown in FIG. 11, first a substrate 301 is provided. The substrate 301may include Si. In addition, the substrate 301 further includes an imagesensor element 302. A first dielectric layer 310 is formed on thesubstrate 301. For example, the procedure of the present invention toform the first dielectric layer 310 may be that a chemical vapordeposition is carried out to form the resultant first dielectric layer310. Later, the first dielectric layer 310 is selectively etched to forma phase grating 330.

The procedure to carry out the selective etching may be that, as shownin FIG. 12, first a patterned mask 340 is formed on the first dielectriclayer 310 to facilitate the selective etching. FIG. 13 illustrates a topview of the patterned mask 340 placed on the first dielectric layer 310.The patterned mask 340 is placed on the first dielectric layer 310 andincludes a concentric center circle 341, and a plurality of concentricrings 342 alternating with the concentric grating zones 343 which arenot covered by the patterned mask 340. The widths of the concentricgrating zones 343 are different. Later, the first dielectric layer 310is etched through the grating zones 343, as shown in FIG. 13.Optionally, the patterned mask 340 is removed after the selectiveetching of the first dielectric layer 310 is completed. Becausedifferent sizes of openings are susceptible to different etchingstrength under the same etching condition, for example in the presenceof an isotropic etching, trenches of different depths are accordinglyformed.

Please refer to FIG. 13. The phase grating 330 includes a column 331 anda plurality of rings 332. The phase grating 330 is disposed above thecorresponding image sensor element 302. A plurality of rings 332alternate with the Fresnel grating zones 333. The column 331 and therings 332 are concentric. The widths of the rings 332 are usually thesame. However, due to the different width of each of the grating zones343, i.e. different area open to the etching, annular trenches 333′ ofdifferent depths are therefore formed. Generally speaking, the largerthe opening, i.e. the widths, the deeper the annular trenches arebecause of a stronger etching driving force. FIG. 13 illustrates thatthe closer to the concentric center, the shallower the annular trenches333′ are, i.e. the narrower the width of the annular trenches 333′ are.Different slopes caused by different depths may have different opticalapplications, for example different colors such as red (R), green (G) orblue (B).

On the other hand, FIG. 14 illustrates that the closer to the concentriccenter, the deeper the annular trenches 333′ are, i.e. the wider thewidths of the annular trenches 333′ are, which causes the annulartrenches 333′ have different depths. This three-dimensionalconfiguration results in the Fresnel-Lens type phase grating of thepresent invention possesses excellent optical properties and focuscapability. In such way, the phase grating of the present invention notonly exhibits the advantage of the Fresnel-Lens but also avoids thedisadvantages of the complicated processes to form semiconductor opticalelements, such as micro lens or color filters.

The method of the present invention ingeniously employs the differencecaused by the deposition/sputter ratio of the deposition operation ofthe semiconductor process, the difference of etching selectivity ofdifferent materials and the difference of etching strengths caused bydifferent opening sizes. FIG. 15 illustrates a cross sectional view ofthe phase grating of the present invention. The phase grating 130 of thepresent invention can be easily and conveniently obtained by means ofselective etching on the patterned layer 103 in the first dielectriclayer 110. The phase grating 130 includes a column 131, a plurality ofrings 132 and the Fresnel grating zones 133. The etching-stop layer 104is also exposed. In such way, the problems which the Fresnel-Lens typephase grating encounters in the semiconductor field are overcome. Still,the micro optical elements, such as the CMOS image sensor (CIS) in thesemiconductor field may also utilize the vantage point of theFresnel-Lens type phase grating well.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A phase grating, comprising: a substrate; a firstdielectric layer having a bulge with a tapered side on said substrate;and a second dielectric layer disposed on said first dielectric layerand comprising a column and a plurality of rings, wherein the top sidesof said column and of said rings align with one another to form a flatplane, said column and said rings are concentric and said rings aredisposed on said tapered side of said bulge so that the height of eachsaid ring is different.
 2. The phase grating of claim 1, wherein saidsubstrate comprises an image sensor to correspond to said phase grating.3. The phase grating of claim 1, wherein said first dielectric layer andsaid second dielectric layer has different etching selectivity.
 4. Thephase grating of claim 1, further comprising: an etching-stop layerdisposed on said first dielectric layer.
 5. The phase grating of claim4, wherein said etching-stop layer is selected from the group consistingof nitride, oxide and oxynitride.
 6. A phase grating, comprising: asubstrate; a first dielectric layer disposed on said substrate andcomprising a column and a plurality of rings, wherein the top sides ofsaid column and of said rings align with one another to form a flatplane, said column and said rings are concentric; and a plurality ofannular trenches respectively sandwiched between said column and saidrings so that the depths of any two annular trenches which are adjacentare different.
 7. The phase grating of claim 6, wherein said substratecomprises an image sensor to correspond to said phase grating.
 8. Thephase grating of claim 6, wherein said annular trenches respectivelyhave different width.
 9. The phase grating of claim 8, wherein thecloser to the concentric center the smaller said width is.
 10. The phasegrating of claim 6, wherein the closer to the concentric center thegreater said depth is.